JP5162163B2 - Wafer laser processing method - Google Patents

Description

  The present invention relates to a laser processing method for irradiating a laser beam along a predetermined division line formed on a wafer such as a semiconductor wafer and forming a deteriorated layer along the predetermined division line inside the wafer.

  In the semiconductor device chip manufacturing process, a plurality of rectangular areas are defined on the surface of a substantially disk-shaped semiconductor wafer by dividing lines arranged in a lattice pattern, and electronic circuits such as ICs and LSIs are formed in these rectangular areas. Alternatively, after forming a microelectromechanical element called MEMS (Micro Electro Mechanical System), the wafer is cut along a division line to obtain a rectangular region as a semiconductor chip. The thickness of the wafer is generally about 600 to 800 μm, and from this thickness, it may be thinned by grinding the back surface as necessary, but it is not thinned depending on the application. In some cases, the wafer is divided in the thickness state.

  As a means for cutting the wafer, a dicing method is generally used in which a thin disk-shaped blade rotated at a high speed is cut into the wafer. This dicing method has an advantage that a flat and sharp cut surface can be obtained. However, the width of the line to be divided between chips needs to be larger than the thickness of the blade to be used (mainly about 10 to 30 μm). Therefore, the cutting allowance is relatively large, which is disadvantageous in terms of improving the productivity by obtaining as many chips as possible per wafer.

  On the other hand, in recent years, a translucent laser beam is irradiated along the planned dividing line to the inside of the wafer to form a deteriorated layer having reduced physical strength, and then an external force is applied to the wafer along the planned dividing line. A laser method has also been adopted in which a wafer is cleaved to obtain individual chips. In this laser method, the cutting allowance is much smaller than that in the dicing method, which is advantageous in terms of productivity. However, when a wafer that has remained relatively thin without being thinned as described above is divided by the laser method, one layer of a deteriorated layer is formed by irradiating a laser beam once on one division planned line. However, the proportion of the deteriorated layer is small compared to the thickness, and may not be divided smoothly.

  In view of this, a technique is known in which a laser beam is irradiated to a plurality of stages on a single division line to form a multi-layered altered layer so that cleaving can be performed easily and precisely (see Patent Document 1). Also proposed is a technique for efficiently forming a deteriorated layer by changing the wavelength of the laser beam to be irradiated from the conventional 1064 nm to 1100 to 2000 nm (preferably 1300 to 1600 nm) with better transparency into the wafer. Has been.

JP 2002-205180 A JP 2006-104859 A

  For example, when a wafer having a thickness of 625 μm is cleaved by irradiating it with a laser beam, a conventional laser beam with a wavelength of 1064 nm requires a multi-layered alteration layer of about 18 layers in the thickness direction of the wafer. In other words, the laser beam irradiation is performed 18 times for one division planned line, and it cannot be said that the processing efficiency is good due to the large number of irradiation times. On the other hand, if a laser beam having a wavelength of 1342 nm is used, the altered layer can be cleaved with about 8 layers, and the processing efficiency is improved. However, even if a laser beam having a wavelength of 1342 nm is irradiated, it is actually difficult to form a multi-layered altered layer close to the thickness direction. When a multi-layered altered layer is formed, it is said that a smooth cleaving can be realized by a crack layer extending from the formed altered layer toward an adjacent altered layer. Therefore, if the multi-layered deteriorated layer cannot be formed close to the cracked layer, it is difficult for the cracked layer to reach the adjacent deteriorated layer, and cleaving failure is likely to occur.

  The reason why it is difficult to form adjacent deteriorated layers close to each other is that strains and defect layers at the crystal level are formed in the vicinity of the once formed deteriorated layer and the crack layer extending from this deteriorated layer. It is presumed that the multi-photon absorption is not sufficiently performed because the light is not condensed well even if the portion is irradiated with the laser beam. For this reason, in the case of forming the second deteriorated layer adjacent to the first deteriorated layer formed earlier, it is inevitably formed to be separated from the crack layer extending from the first deteriorated layer to some extent. The crack layer extending from the first deteriorated layer does not reach the second deteriorated layer, so that cleaving defects are likely to occur.

  Therefore, an object of the present invention is to provide a wafer laser processing method capable of cleaving a wafer easily and reliably without lowering the processing efficiency.

In the present invention, when performing laser beam irradiation operation for irradiating a laser beam to the inside of the wafer from one side of the wafer along a predetermined division line formed on the wafer a plurality of times, each time the operation is performed, the laser beam A wafer laser processing method in which a plurality of deteriorated layers along a planned dividing line are formed in a wafer in a thickness direction by changing a focal position of the wafer stepwise in an incident direction. , the holder, move the other surface of the wafer, and the pulsed laser beam and the wafer holding step of holding to expose the one side, the laser beam irradiation operation, over one surface side from the other surface side of the wafer held in the holder by the irradiation several times, leaving the affected layer, a plurality of composite layers consisting of a crack layer extending on one side direction from the modified electrolyte layer, a distance to the incident direction A first laser beam irradiation step of stepwise formation, illuminated by the first between a plurality of composite layers formed by laser beam irradiation step, the first laser beam irradiation step focused position of the laser beam A second laser beam irradiation step of irradiating a pulse laser beam having the same wavelength as that of the laser beam repeated a plurality of times , thereby extending the crack layer in one surface direction and reaching the altered layer adjacent in the direction; And a wafer cleaving step of cleaving the wafer along a division line by applying an external force to the wafer after the laser beam irradiation step.

According to the present invention, there is no crack layer between the plurality of composite layers (modified layer + crack layer) formed in the wafer by the first laser beam irradiation step, but the crystal extending from the crack layer Even if the laser beam is irradiated due to the influence of defects or the like, multiphoton absorption is not performed, and an altered layer is difficult to form. However, the effect | action which extends the crack layer extended from the already existing altered layer by irradiation of a laser beam is anticipated. In the second laser beam irradiation step, the non-crack layer is irradiated with a laser beam, and the crack layer is stretched to the deteriorated layer of the adjacent composite layer. As a result, the crack layer can reach the altered layer. For this reason, when a wafer is cleaved in the wafer cleaving process, the cleaving can be performed easily and smoothly, and no cleaving failure is caused. In the present invention, by performing the second laser beam irradiation step, the number of altered layers formed by the first laser beam irradiation step can be reduced, and the total number of laser beam irradiations by both steps is also as follows. This can be reduced from the conventional number of times of laser beam irradiation that can be cleaved. For this reason, a decrease in processing efficiency can be suppressed.

  In the second laser beam irradiation step, it is not necessary to irradiate all the non-crack layers between the composite layers with laser beams, and the cleaving is possible even if the non-crack layers selected appropriately are irradiated. Thus, when not irradiating all the non-crack layers with a laser beam in the second laser beam irradiation step, the processing efficiency can be further improved.

  In the present invention, the wavelength of the laser beam applied to the inside of the wafer is set to 1100 to 2000 nm, preferably 1300 to 1600 nm, because the transparency to the inside of the wafer is better and the processing efficiency is further improved. It is suitable from the viewpoint of being able to.

  According to the present invention, a laser beam is irradiated with the focal position of the laser beam being adjusted between the plurality of composite layers (modified layer + crack layer) formed in the first laser beam irradiation step (second laser beam). (Irradiation step), the crack layer can be extended to reach the deteriorated layer of the adjacent composite layer, and thereby the wafer can be cleaved easily and reliably without reducing the processing efficiency. There are effects such as.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.
[1] Semiconductor wafer Reference numeral 1 in FIG. 1 indicates a disk-shaped semiconductor wafer having a relatively large thickness dimension of about 600 to 800 μm. A plurality of rectangular semiconductor chips (devices) 3 are defined on the surface of the wafer 1 by grid-like division lines 2, and on the surface of the semiconductor chips 3, an unillustrated electronic device such as an IC or LSI is provided. A circuit is formed. A V-shaped notch 4 indicating the crystal orientation of the semiconductor is formed at a predetermined location on the peripheral surface of the wafer 1.

  A wafer 1 is irradiated with a laser beam along a predetermined division line 2 by the laser processing method according to an embodiment of the present invention to form a deteriorated layer, and the deteriorated layer is cut into individual semiconductor chips 3. It is separated. The laser processing method of one embodiment is suitably implemented using the laser processing apparatus shown in FIG.

[2] Formation of Altered Layer by Laser Processing Device The wafer 1 is held on a horizontal chuck table 11 provided in the laser processing device 10 with the surface side on which the semiconductor chip 3 is formed facing upward (wafer holding). Process). A laser head 21 that irradiates a laser beam vertically downward is disposed above the chuck table 11. The chuck table 11 is installed on an XY movement table 13 provided on the base 12 of the apparatus 10 so as to be movable in the horizontal X-axis direction and the Y-axis direction. By moving in the axial direction, a laser beam is irradiated from the laser head 21 to the planned division line 2.

  The XY moving table 13 includes an X-axis base 30 provided on the base 12 so as to be movable in the X-axis direction, and a Y-axis base 40 provided on the X-axis base 30 so as to be movable in the Y-axis direction. It consists of a combination. The X-axis base 30 is slidably attached to a pair of parallel guide rails 31 that are fixed on the base 12 and extend in the X-axis direction, and an X-axis drive mechanism 34 that operates a ball screw 33 by a motor 32. Is moved in the X-axis direction. On the other hand, the Y-axis base 40 is slidably attached to a pair of parallel guide rails 41 extending in the Y-axis direction fixed on the X-axis base 30, and the Y-axis that operates the ball screw 43 by the motor 42. It is moved in the Y-axis direction by the drive mechanism 44.

  The chuck table 11 is of a generally known vacuum chuck type that holds a workpiece (in this case, the wafer 1) by vacuum action and is rotatably supported on the Y-axis base 40 and is not shown. It can be rotated in one direction or both directions by a rotating drive mechanism. The chuck table 11 is moved in the X-axis direction and the Y-axis direction as the X-axis base 30 and the Y-axis base 40 move.

  The wafer 1 held on the chuck table 11 is rotated by rotating the chuck table 11 so that each division planned line 2 extending in one direction is parallel to the X-axis direction and each division planned extending in the other direction perpendicular thereto. The line 2 is parallel to the Y-axis direction, and this state is fixed by stopping the chuck table 11. While maintaining this state, the X-axis base 30 and the Y-axis base 40 of the XY moving table 13 are appropriately moved, and the laser beam emitted from the laser head 21 is projected from the surface side along the scheduled division line 2. The inside of the wafer 1 is irradiated. In the present embodiment, the focal position of the laser beam is set inside the wafer 1, and the altered layer is formed at the focal position.

  The laser head 21 is provided at the tip of a casing 22 that extends in the Y-axis direction toward the chuck table 11. The casing 22 is provided on the column 14 erected on the upper surface of the base 11 so as to be movable up and down along the vertical direction (Z-axis direction), and is driven up and down (not shown) housed in the column 14. It is moved up and down by the mechanism.

  The laser head 21 is connected to a pulse laser oscillator composed of a YAG laser oscillator or a YVO4 laser oscillator so that the laser oscillated by the laser oscillator is irradiated as a laser beam vertically downward from the laser head 21. It has become. The laser oscillated by the laser oscillator has good transparency to the inside of the wafer and forms a deteriorated layer with certainty so that it can be easily cleaved. For example, the output is 1 to 5 W, the wavelength is 1100 to 2000 nm, preferably What has the characteristic of 1300-1600 nm is used suitably.

  The irradiation position of the laser beam from the laser head 21 is controlled based on the imaging of the microscope 24 attached to one side of the casing 22 via the arm 23. The microscope 24 moves up and down together with the laser head 21 as the casing 22 moves up and down to adjust the focus. Prior to laser beam irradiation, the wafer 1 held on the chuck table 11 is moved below the microscope 24 and a surface pattern image is taken by the microscope 24. Then, the imaged pattern image of the wafer surface is taken in by an image processing means (not shown), and the division line 2 to be cut is detected by the image processing means. Further, based on the data of the planned division line 2 detected by the image processing means, the movement operation of the chuck table 11 and the XY movement table 13 and the operation of laser beam irradiation from the laser head 21 are controlled. If an infrared microscope is used as the microscope 24, the back surface side is exposed and the wafer 1 is held on the chuck table 11, and in this state, the inside of the wafer 1 is transmitted from the back surface of the wafer 1 and a pattern image of the surface is captured. Thus, it is possible to recognize the division planned line 2. Thereby, it is possible to irradiate the laser beam from the back side of the wafer 1.

  In the laser processing apparatus 10 described above, the laser beam is irradiated from the laser head 21 onto the planned division line 2 while moving the X-axis base 30 in the X-axis direction, thereby causing the wafer along the planned division line 2 parallel to the X-axis direction. An altered layer is formed inside. Further, by irradiating the laser beam from the laser head 21 to the planned division line 2 while moving the Y-axis base 40 in the Y-axis direction, an altered layer is formed inside the wafer along the planned division line 2 parallel to the Y-axis direction. It is formed. When irradiating the laser beam, the casing 22 is moved up and down to adjust the vertical position of the laser head 21 in order to form a deteriorated layer by aligning the focal point inside the wafer. Is set to the target height.

  As described above, the laser beam is irradiated along all the planned division lines 2 parallel to the X-axis direction and the Y-axis direction to form a deteriorated layer inside the wafer. The laser beam irradiation operation for the division line 2 is performed a plurality of times, and each time this operation is repeated, the focal position of the laser beam is stepped from the vicinity of the back surface of the wafer 1 near the chuck table 11 to the front surface side. As shown in FIG. 3, a plurality of altered layers 50 are formed (first laser beam irradiation step). Further, after this step, a laser beam is irradiated between the plurality of altered layers 50 (second laser beam irradiation step). Below, these processes are explained in full detail.

[2-1] First Laser Beam Irradiation Step As shown in FIG. 4A, the focal point of the laser beam L at a height position in the vicinity of the back surface 1b of the inside of the wafer 1 in one division line 2. The alignment is performed, and the laser beam L is irradiated horizontally along the planned division line 2 to form the deteriorated layer 50 (first deteriorated layer 50a). As the altered layer 50a is formed, a crack layer 51 composed of a number of cracks extending from the altered layer 50a to the upper surface side is formed. Here, the first deteriorated layer 50a and the crack layer 51 derived from the first deteriorated layer 50a are referred to as a composite layer (first composite layer 52A) 52.

  Next, as shown in FIG. 4B, a plurality of composite layers 52 are formed by irradiating the laser beam L stepwise over the first composite layer 52A (on the wafer surface 1a side) at intervals. To do. In this case, five composite layers 52 (first to fifth composite layers 52A, 52B, 52C, 52D, and 52E) are formed, and these composite layers 52 (52A to 52E) are formed of the first to fifth composite layers 52 (52A to 52E). The crack layer 51 is derived from the altered layers 50a, 50b, 50c, 50d, and 50e. Further, the intervals between the composite layers 52 are uniform, and the intervals are always ensured, and the interval in the thickness direction of the focal position of the laser beam for that purpose is, for example, about 20 μm. In the first laser beam irradiation step, the focal position of the laser beam irradiated immediately above the composite layer 52 is set above the crack layer 51 of the composite layer 52 immediately below, and therefore the crack layer 51 is interposed between the composite layers 52. A non-cracking layer 53 that does not exist is provided. Note that the composite layer 52 is not formed over the entire thickness of the wafer 1, and a predetermined gap is provided between the composite layer 52 on the most surface side and the surface 1a. This is because the semiconductor chip 3 formed on the surface 1a is not damaged by the laser beam.

[2-2] Second Laser Beam Irradiation Step As shown in FIG. 4C, the non-crack layer 53 between the composite layer 52A closest to the back surface 1b of the wafer 1 and the composite layer 52B thereon. Then, the laser beam L is irradiated with the focal position adjusted. As a result, the crack layer 51 formed during the formation of the deteriorated layer 50a extends upward, and the extended crack layer 54 reaches the upper deteriorated layer 50b. The irradiation of the laser beam L to the non-crack layer 53 is performed on the non-crack layer 53 between the composite layers 52 as shown in FIG. In the case of the figure, the laser beam is not radiated to the non-crack layer 53 between the composite layers 52C and 52D, but the laser beam may be irradiated to the non-crack layer 53 between all the composite layers 52. Good.

  In this way, a plurality of composite layers 52 are formed on one division line 2, and the non-crack layer 53 between these composite layers 52 is appropriately irradiated with the laser beam L so that the crack layer 51 is adjacent. By reaching the deteriorated layer 50, the subsequent wafer cleaving operation can be performed easily and reliably.

  For example, for a wafer having a diameter of about 150 mm and a thickness of about 400 μm and a semiconductor chip 3 having a size of about 1.5 mm, the first and second laser beam irradiation processes are performed in the same manner as described above to form a composite of five layers. By forming the layer 52 and forming the three extended crack layers 54, the wafer can be easily cut. The irradiation condition of the laser beam at this time is a pulse laser with a laser beam wavelength of 1342 nm, the repetition frequency is 150 kHz, the NA (numerical aperture) of the condensing lens of the laser beam is 0.8, and the moving speed of the chuck table 11 ( The machining feed rate by the XY table 13) is 300 mm / sec.

Irradiation of the laser beam to the non-crack layer 53 is performed in a plurality of times by reciprocating the XY table 13. Further, the wavelength of the laser beam for forming the deteriorated layer 50 in the first laser beam irradiation step is the same as the wavelength of the laser beam irradiated on the non-crack layer 53 in the second laser beam irradiation step . The laser beam applied to the laser beam and a non-crack layer 53 for forming a variable electrolyte layer 50 are both a pulsed laser beam. Further, the NA (numerical aperture) of the condensing lens of the laser beam applied to the non-crack layer 53 is preferably the same as or smaller than that of the laser beam for forming the altered layer 50.

  As described above, a plurality of composite layers (modified layer 50 + crack layer 51) 52 are formed for all the division lines 2 extending in the X-axis direction and the Y-axis direction. When the stretched crack layer 54 is formed by irradiating the laser beam L to all the non-crack layers 53 or appropriately selected non-crack layers 53, the wafer 1 is removed from the chuck table 11, and the next wafer cleaving process is started.

  As shown in FIG. 5, the wafer 1 is cleaved by attaching the back side of the wafer 1 to a dicing tape 62 having a dicing frame 61 attached around it. The broken line in the figure shows the division line 2 in which the composite layer (modified layer 50 + crack layer 51) 52 and the stretched crack layer 54 are formed. The wafer 1 is set on an external force applying device such as a braking device via a dicing tape 62 and a dicing frame 61, and an external force such as applying a tension to the dicing tape 62 is applied, so that the division line 2 is formed. The semiconductor chips 3 are divided into individual pieces.

[3] Advantageous Effects of One Embodiment According to the one embodiment, cracks are not formed between the plurality of composite layers (modified layer 50 + crack layer 51) 52 formed in the wafer by the first laser beam irradiation step. The layer is a non-cracked layer 53 in which no layer is present, but this portion is not subjected to multiphoton absorption even when irradiated with a laser beam due to the influence of crystal defects or the like extending from the crack layer 51, and the altered layer is difficult to form. . However, the effect | action which extends the crack layer 51 extended from the alteration layer 50 which already exists by irradiation of a laser beam is anticipated. In the second laser beam irradiation step, the non-crack layer 53 is irradiated with a laser beam to extend the crack layer 51 to the adjacent altered layer 50. As a result, the crack layer 51 formed in the first laser beam irradiation step reaches the adjacent deteriorated layer 50, so that the wafer 1 can be cleaved easily and smoothly, resulting in cleaving failure. There is an effect that there is nothing.

  Further, by performing the second laser beam irradiation step, the number of altered layers 50 formed by the first laser beam irradiation step can be reduced, and the total number of laser beam irradiations by both steps is also the same as the conventional number. The number of times of laser beam irradiation that can be cut can be reduced. For this reason, a decrease in processing efficiency can be suppressed. Further, it is not necessary to irradiate all the non-crack layers 53 between the composite layers 52 with a laser beam, and it is possible to cleave even if the non-crack layer 53 selected appropriately is irradiated. When not irradiating all the non-crack layers 53 with the laser beam in the light beam irradiation step, the processing efficiency can be further improved.

Next, examples of the present invention will be described to demonstrate the effects of the present invention. The number of wafer samples prepared in the following examples and comparative examples is 10 each.
[Example 1]
A sample silicon wafer having a diameter of 150 mm and a thickness of 400 μm was used as a sample. This wafer is a so-called “mirror wafer” in which a device pattern is not formed on the surface such that an electronic circuit is provided in a chip region formed by a grid-like division line. This wafer was set on the chuck table of a laser processing apparatus similar to that shown in FIG. Then, virtual splitting lines with an interval of 1.5 mm are set on this wafer, and five composite layers (modified layers + crack layers) are placed on all the virtual splitting lines at a distance of 20 μm from the position close to the back surface. Then, three of the four non-crack layers between the composite layers were irradiated with a laser beam to form a stretched crack layer. That is, the laser beam irradiation operation was performed 8 times for one division planned line. The laser beam was a pulse laser, and the irradiation conditions were as follows.

Light source: LD excitation Q switch Nd: YVO4 laser Wavelength: 1342 nm
・ Repetition frequency: 150 kHz
-Output: Output 1.2W (0.6W when forming the most surface side composite layer)
・ NA (numerical aperture) of condensing lens of laser beam ... 0.8
・ Movement speed of chuck table (processing feed speed) ... 300mm / sec
・ Pulse width: 105ns
・ Condensing spot diameter: φ1.5μm

[Example 2]
On the surface of the mirror wafer similar to that in Example 1, a grid-like division planned line is actually formed at an interval of 1.5 mm, and an appropriate electronic circuit is formed in a chip area partitioned by the division planned line, A “pattern wafer” on which a device pattern was formed was obtained as a sample. This wafer was irradiated with a laser beam in exactly the same manner as in Example 1 to form 5 composite layers (modified layer + crack layer) + 3 stretched non-crack layers inside all the division lines. did.

[Comparative Example 1]
For the same mirror wafer as in Example 1, the output of the laser beam for forming the composite layer is 0.8 W (0.5 W when forming the composite layer on the most surface side), and 8 composite layers are formed. Only the composite layer of 8 layers was formed in the division | segmentation schedule line on the conditions which do not irradiate a laser beam between composite layers on the conditions similar to Example 1 except this.

[Comparative Example 2]
The same pattern wafer as in Example 2 was irradiated with a laser beam under exactly the same conditions as in Comparative Example 1, and only 8 composite layers were formed on the planned division lines.

[Comparative Example 3]
For the same mirror wafer as in Example 1, the output of the laser beam for forming the composite layer is 1.2 W (0.6 W when forming the composite layer on the most surface side), and 5 composite layers are formed. Only the composite layer of 5 layers was formed in the division | segmentation schedule line on the conditions which do not irradiate a laser beam between composite layers on the conditions similar to Example 1 except this.

[Comparative Example 4]
The same pattern wafer as in Example 2 was irradiated with a laser beam under exactly the same conditions as in Comparative Example 3, and only five composite layers were formed on the planned division lines.

[Cleaving test]
Ten wafers of each of Examples 1 and 2 and Comparative Examples 1 to 4 are attached to a dicing tape as shown in FIG. 5, set on a braking device and applied with external force to try to cleave the wafer. It was. The result of the cleaving situation was as follows. The cleaving rate is defined as 100% when all the semiconductor chips formed on one wafer are divided and separated into individual pieces. Moreover, the result of observing the fractured surface was added.

-Cleaving rate Example 1 (mirror wafer) ... Cleaving rate: 100%
Example 2 (pattern wafer) ... Cleaving rate: 100%
Comparative Example 1 (mirror wafer) ... Cleaving rate: 90%
Comparative example 2 (pattern wafer) * Not implemented Comparative example 3 (mirror wafer) ... Cleaving rate: 100%
Comparative Example 4 (pattern wafer) ... 2% of 10 out of 2 cracks remaining on 2 sheets

-State of fractured surface The fractured surfaces of Examples 1 and 2 and Comparative Examples 3 and 4 with 5 altered layers are almost the same, and the alternating stripe pattern of the altered layer and the crystalline layer (non-cracked layer) is clearly observed. It was done. This is probably because the number of deteriorated layers relative to the wafer thickness is relatively small and the interval between the deteriorated layers is large. On the other hand, in Comparative Examples 1 and 2 having 8 deteriorated layers, since the number of deteriorated layers was large, adjacent deteriorated layers appeared to be quite close and continuous.

  According to said result, Example 1, 2 based on this invention showed the favorable result with a cleaving rate of 100%. On the other hand, in Comparative Examples 3 and 4 in which the laser beam irradiation to the altered layer performed in Examples 1 and 2 was omitted, although the cleaving rate was 100% in the relatively easily cleaved mirror wafer (Comparative Example 3), The pattern wafer (Comparative Example 4) that is difficult to cleave could not obtain 100%. Thereby, the effect of the present invention by irradiating the non-cracked layer between the altered layers with a laser beam to reach the altered layer was demonstrated. Further, in Comparative Examples 1 and 2, the mirror wafer had a cleaving rate of 90%, and a reduction in the cleaving rate due to the relatively dense formation of the altered layer was observed. In addition, since the pattern wafer of Comparative Example 2 is more difficult to cleave than a mirror wafer, the cleaving rate cannot be expected to exceed 90%, and therefore cleaving was not performed.

1 is a perspective view of a semiconductor wafer separated into a plurality of semiconductor chips according to an embodiment of the present invention. 1 is an overall perspective view of a laser processing apparatus that can suitably perform a method according to an embodiment of the present invention. It is a see-through | perspective perspective view which shows typically the state which formed the multiple layer alteration layer in the wafer along the division | segmentation planned line. It is the cross-sectional enlarged view of the wafer which shows the method which concerns on one Embodiment in order of (a)-(d). It is a perspective view which shows the state which stuck this wafer to the dicing tape in order to cleave the wafer which irradiated the laser beam to the division | segmentation planned line.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor wafer 1a ... Wafer surface (one side)
1b ... Back side of wafer (other side)
2 ... Scheduled line 3 ... Semiconductor chip 10 ... Laser processing apparatus 11 ... Chuck table (holding table)
50 ... Altered layer 51 ... Crack layer 54 ... Stretched crack layer 52 ... Composite layer 53 ... Non-crack layer L ... Laser beam

Claims (2)

When the laser beam irradiation operation for irradiating the laser beam to the inside of the wafer from one side of the wafer along the planned division line formed on the wafer is performed a plurality of times, the focal position of the laser beam is changed each time the operation is performed. A method of laser processing a wafer, wherein a plurality of altered layers along a predetermined division line are formed in the wafer in a stepwise manner in the incident direction, thereby forming a plurality of altered layers in the thickness direction of the wafer,
A wafer holding step for aligning the other surface of the wafer with the holding table and exposing and holding one surface,
The laser beam irradiation operation is performed by irradiating a pulse laser beam a plurality of times from the other surface side to the one surface side of the wafer held on the holding table, thereby causing the deteriorated layer and a crack layer extending in one surface direction from the deteriorated layer. A first laser beam irradiation step of forming a plurality of composite layers consisting of: stepwise with an interval in the incident direction;
A pulse laser beam having the same wavelength as that of the laser beam irradiated in the first laser beam irradiation step with the focal position of the laser beam being aligned between the plurality of composite layers formed in the first laser beam irradiation step a plurality of times. A second laser beam irradiation step of extending the crack layer in the one surface direction to reach the altered layer adjacent in the direction,
A wafer laser processing method comprising a wafer cleaving step of applying an external force to the wafer and cleaving the wafer along the planned division line after the second laser beam irradiation step.   2. The wafer laser processing method according to claim 1, wherein the wavelength of the laser beam is set to 1100 to 2000 nm.

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